GAS PIPE LINE CALCULATION SIZING

GAS PIPE LINE CALCULATION SIZING

USING CPC PIPE SIZING TABLE (NATURAL GAS)

This handout will guide you thru the basic, most common method for sizing a natural gas piping system for residential or commercial application. There are other methods available for sizing these systems by either a complex formulaic method described in the California Plumbing Code, or the system can be engineered by a qualified professional. The information below is paraphrased from the California Plumbing Code and is provided as an aid.

Sizing of Gas Piping Systems. Gas piping systems shall be of such size and so installed as to provide a supply of gas to meet the maximum demand and supply gas to each appliance inlet at not less than the minimum supply pressure required by the appliance.

Required Gas Supply. Volume. The hourly volume of gas required at each piping outlet shall be taken as not less than the maximum hourly rating as specified by the manufacturer of the appliance or appliances to be connected to each such outlet. Where the rating of the gas appliance(s) to be installed is unknown, Table 1 shall be permitted to be used to estimate requirements of typical appliances. To obtain the cubic feet per hour of gas required, divide the input of the appliances by the average Btu (kW.h) heating value per cubic foot of the gas. The average Btu per cubic foot is 1,100.

Longest Length Method. The size of each section of gas piping shall be determined using the total length of piping from the meter to the most remote outlet and the load of that section (see calculation example in "Figure A" use steps 1- 6 below:

Sizing of Piping Sections To determine the size of each section of pipe in any system using piping specific table*, and proceed as follows: (1) Measure the length of the pipe from the gas meter location to the most remote outlet on the system. (2) Locate that total length in the left-hand column of sizing table*, or the next longer distance where the table does not give the exact length. (3) Starting at the most remote outlet, find in the row just selected the gas demand for the outlet. Where the exact figure of demand is not shown, choose the next larger figure in the row. (4) At the top of this column will be found the correct size of pipe. (5) Using this same row, proceed in a similar manner for each section of pipe serving this outlet. For each section of pipe, determine the total gas demand supplied by that section. (6) Size each section of branch piping not previously sized by measuring the distance from the gas meter location to the most remote outlet in that branch and follow the procedures of steps 2, 3, 4, and 5 above. Size branch piping in the order of their distance from the meter location, beginning with the most distant outlet not previously sized.

*See Pipe Specific Tables on pages 4, 5, and 6. 1

TABLE 1

APPROXIMATE GAS INPUT FOR TYPICAL APPLIANCES

APPLIANCE

INPUT Btu/h. (Approx.)

Cubic Feet of Gas Per Hour

Space Heating Units

Warm air furnaces:

Single family

100,000

91

Multifamily, per unit

60,000

55

Hydronic boilers:

Single family

100,000

91

Multifamily, per unit

60,000

55

Space and Water-Heating Units

Hydronic boilers:

Single family

120,000

109

Multifamily, per unit

75,000

68

Water-Heating Appliances

Water heater, automatic:

Storage 30 to 40 gal. tank

35,000

32

Water heater, automatic

Storage 50 gal. tank

50,000

45

Water heater, automatic instantaneous:

Capacity at 2 gal./minute

142,800

130

Capacity at 4 gal./minute

285,000

259

Capacity at 6 gal./minute

428,400

389

Water heater, domestic

Circulation or side-arm

35,000

32

Cooking Appliances

Range, freestanding, domestic

65,000

59

Built-in oven/ broiler, domestic

25,000

23

Built-in counter-top range, domestic

40,000

36

Other Appliances

Clothes dryer, domestic

35,000

32

Gas fireplace ? direct vent

40,000

36

Gas log unit

80,000

73

Barbecue

40,000

36

Gas Refrigerator

3,000

2

For SI units: 1 Btu per hour = .0293 W *Maximum gas demand of outlet A = 31 CFH (35,000 btu/hr divided by 1100 btu per cubic foot

2

Method for determining correct pipe sizing per 1216.1.1:

(1) Compute CFM demand for all appliances

Maximum gas demand of outlet A: 32 cubic feet per hour (from Table 1).

35,000BTU/1,100 BTU2 = 32

Maximum gas demand of outlet B:

3000/1,100 = 3

3 cubic feet per hour (from Table 1).

65,000/1,100 = 59

Maximum gas demand of outlet C:

59 cubic feet per hour (from Table 1).

Maximum gas demand of outlet D:

136 cubic feet per hour [150,000 Btu/hour divided by 1100 Btu per cubic foot].

(2) Determine the length of pipe from the gas meter to the most remote outlet (outlet A) is 60 feet.

Sec 1 (10) + Sec 2 (10) + Sec 3 (30) = 60

(3) Using the length in feet column row marked 60 feet in Table 2* for type of pipe: Outlet A, supplying 32 cubic feet per hour, requires ? inch pipe. Section 1, supplying outlets A and B, or 35 cubic feet per hour requires ? inch pipe. Section 2, supplying outlets A, B, and C, or 94 cubic feet per hour requires 3/4 inch pipe. Section 3, supplying outlets A, B, C, and D, or 230 cubic feet per hour, requires 1 inch pipe.

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